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1
Ban, Zhen Hong, Kok Keong Lau, and Mohd Sharif Azmi. "Bubble Nucleation and Growth of Dissolved Gas in Solution Flowing across a Cavitating Nozzle." Applied Mechanics and Materials 773-774 (July 2015): 304–8. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.304.
Повний текст джерелаАнотація:
Computational modelling of dissolved gas bubble formation and growth in supersaturated solution is essential for various engineering applications, including flash vaporisation of petroleum crude oil. The common mathematical modelling of bubbly flow only caters for single liquid and its vapour, which is known as cavitation. This work aims to simulate the bubble nucleation and growth of dissolved CO2 in water across a cavitating nozzle. The dynamics of bubble nucleation and growth phenomenon will be predicted based on the hydrodynamics in the computational domain. The complex interrelated bubble dynamics, mass transfer and hydrodynamics was coupled by using Computational Fluid Dynamics (CFD) and bubble nucleation and growth model. Generally, the bubbles nucleate at the throat of the nozzle and grow along with the flow. Therefore, only the region after the throat of the nozzle has bubbles. This approach is expected to be useful for various types of bubbly flow modelling in supersaturated condition.
2
Nguyen, Van Luc, Tomohiro Degawa, and Tomomi Uchiyama. "Numerical simulation of annular bubble plume by vortex in cell method." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 3 (March 4, 2019): 1103–31. http://dx.doi.org/10.1108/hff-03-2018-0094.
Повний текст джерелаАнотація:
PurposeThis study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.Design/methodology/approachThe bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-L–L) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase.FindingsFirst, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-L–L approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation.Originality/valueThe semi-L–L approach is applied to the simulation of the gas–liquid two-phase flows.
3
WANG, Q. X., and J. R. BLAKE. "Non-spherical bubble dynamics in a compressible liquid. Part 1. Travelling acoustic wave." Journal of Fluid Mechanics 659 (July 27, 2010): 191–224. http://dx.doi.org/10.1017/s0022112010002430.
Повний текст джерелаАнотація:
Micro-cavitation bubbles generated by ultrasound have wide and important applications in medical ultrasonics and sonochemistry. An approximate theory is developed for nonlinear and non-spherical bubbles in a compressible liquid by using the method of matched asymptotic expansions. The perturbation is performed to the second order in terms of a small parameter, the bubble-wall Mach number. The inner flow near the bubble can be approximated as incompressible at the first and second orders, leading to the use of Laplace's equation, whereas the outer flow far away from the bubble can be described by the linear wave equation, also for the first and second orders. Matching between the two expansions provides the model for the non-spherical bubble behaviour in a compressible fluid. A numerical model using the mixed Eulerian–Lagrangian method and a modified boundary integral method is used to obtain the evolving bubble shapes. The primary advantage of this method is its computational efficiency over using the wave equation throughout the fluid domain. The numerical model is validated against the Keller–Herring equation for spherical bubbles in weakly compressible liquids with excellent agreement being obtained for the bubble radius evolution up to the fourth oscillation. Numerical analyses are further performed for non-spherical oscillating acoustic bubbles. Bubble evolution and jet formation are simulated. Outputs also include the bubble volume, bubble displacement, Kelvin impulse and liquid jet tip velocity. Bubble behaviour is studied in terms of the wave frequency and amplitude. Particular attention is paid to the conditions if/when the bubble jet is formed and when the bubble becomes multiply connected, often forming a toroidal bubble. When subjected to a weak acoustic wave, bubble jets may develop at the two poles of the bubble surface after several cycles of oscillations. A resonant phenomenon occurs when the wave frequency is equal to the natural oscillation frequency of the bubble. When subjected to a strong acoustic wave, a vigorous liquid jet develops along the direction of wave propagation in only a few cycles of the acoustic wave.
4
Wang, Ping-Ping, A.-Man Zhang, Xiang-Li Fang, Abbas Khayyer, and Zi-Fei Meng. "Axisymmetric Riemann–smoothed particle hydrodynamics modeling of high-pressure bubble dynamics with a simple shifting scheme." Physics of Fluids 34, no. 11 (November 2022): 112122. http://dx.doi.org/10.1063/5.0123106.
Повний текст джерелаАнотація:
High-pressure bubble dynamics often involves many complex issues, including large deformations and inhomogeneities, strong compression, moving interfaces, and large discontinuities, that bring challenges to numerical simulations. In this work, an axisymmetric Riemann–smoothed particle hydrodynamics (SPH) method is used to simulate high-pressure bubbles near different boundaries. This Riemann–SPH can adopt the real sound speed instead of the artificial one for the air phase in the bubble. Therefore, the real compressibility of the air phase can be considered, and the corresponding time step is significantly increased. To avoid unphysical interface penetration and maintain relatively homogeneous particle distribution, a new and simple particle shifting scheme for multiphase flows is proposed. Additionally, to minimize the influence of the unphysical boundary on the bubble, a large fluid domain with an optimized initial particle distribution is adopted to reduce the particle number. Several high-pressure bubbles under different boundary conditions are considered, including in a free field, near a free surface, near a solid boundary, and near a rigid sphere. Numerical results show that these bubble dynamic behaviors can be reproduced with satisfactory accuracy.
5
Chahine, Georges L., and Ramani Duraiswami. "Dynamical Interactions in a Multi-Bubble Cloud." Journal of Fluids Engineering 114, no. 4 (December 1, 1992): 680–86. http://dx.doi.org/10.1115/1.2910085.
Повний текст джерелаАнотація:
Results of studies on the dynamics of “clouds” of bubbles via both an analytical technique using asymptotic expansions, and via numerical simulation using a three-dimensional boundary element technique (BEM) are reported. The asymptotic method relies on the assumption that the characteristic bubble size is much smaller than the characteristic inter-bubble distance. Results obtained from the two methods are compared, and are found to agree in the domain of validity of the asymptotic technique, which is for very low void fractions. Next, results of several numerical experiments conducted using the BEM algorithm are reported. The results indicate the influence of the mutual interaction on the dynamics of multiple bubble clouds.
6
Tao, Sijia, Guangtai Shi, Yexiang Xiao, Zongliu Huang, and Haigang Wen. "Effect of Operating Parameters on the Coalescence and Breakup of Bubbles in a Multiphase Pump Based on a CFD-PBM Coupled Model." Journal of Marine Science and Engineering 10, no. 11 (November 8, 2022): 1693. http://dx.doi.org/10.3390/jmse10111693.
Повний текст джерелаАнотація:
When the multiphase pump is running, the internal medium often exists as bubble flow. In order to investigate the bubble occurrence characteristics in the pressurization unit of the multiphase pump more accurately, this paper couples computational fluid dynamics (CFD) with a population balance model (PBM) to investigate the bubble size distribution law of the multiphase pump under different operating conditions, taking into account the bubble coalescence and breakup. The research shows that the mean bubble size in the impeller domain gradually decreases from 1.7013 mm at the inlet to 0.6179 mm at the outlet along the axis direction; the average bubble diameter in the diffuser domain fluctuates around 0.60 mm. The bubbles in the impeller region gradually change from the trend of coalescence to the trend of breakup along the axial and radial directions, and the bubbles in the diffuser tend to be broken by the vortex entrainment. The bubble size development law is influenced by the inlet gas volume fraction (IGVF) and the rotational speed, showing a more obvious rule, where the gas phase aggregation phenomenon enhanced by the increase in IGVF promotes the trend of bubble coalescence and makes the bubble size gradually increase. The increased blade shearing effect with the increase in rotational speed promotes the trend of bubble breakup, which gradually reduces the size of the bubbles. In addition, increasing the bubble coalescence probability is a key factor leading to changes in bubble size; the bubble size development law is not very sensitive to changes in flow, and the bubble size is at its maximum under design conditions. The research results can accurately predict the performance change of the multiphase pump and provide technical guidance for its safe operation and optimal design.
7
Speidel, S., S. Iwata, and S. Uchiyama. "Dynamics of stripe domain walls in bubble films." Journal of the Magnetics Society of Japan 10, no. 2 (1986): 125–28. http://dx.doi.org/10.3379/jmsjmag.10.125.
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Speidel, S., S. Iwata, and S. Uchiyama. "Dynamics of Stripe Domain Walls in Bubble Films." IEEE Translation Journal on Magnetics in Japan 2, no. 6 (June 1987): 505–11. http://dx.doi.org/10.1109/tjmj.1987.4549508.
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Sedlář, Milan, Patrik Zima, and Martin Komárek. "Numerical Prediction of Erosive Potential of Unsteady Cavitating Flow around Hydrofoil." Applied Mechanics and Materials 565 (June 2014): 156–63. http://dx.doi.org/10.4028/www.scientific.net/amm.565.156.
Повний текст джерелаАнотація:
The paper attempts to assess the erosive potential of cavitation bubbles in unsteady flow of liquid over a prismatic hydrofoil using two-way coupling of the URANS and the Rayleigh-Plesset equations. The erosive potential of the cavitating flow is evaluated from the energy dissipated during the collapses of imploding cavitation bubbles near the solid surface of the hydrofoil. The bubbles are assumed spherical and the phase slip is neglected. Bubble fission is modelled using a simple break-up model. The interaction between bubbles is considered by superposing the pressure change due to pressure waves generated by collapsing bubbles and propagated in the computational domain over the local pressure in the liquid (external to the bubble). The rate of erosion of the solid material is not studied in this work. The flow is analysed using the in-house three-dimensional solver for unsteady turbulent flow with bubble dynamics. The results are demonstrated on the NACA 2412 hydrofoil with the incidence angle of 8 degrees and the cavitation number 1.37, which corresponds to the regime of oscillating partial cavity with periodic shedding of bubble cloud downstream of the cavity.
10
Hou, Jiacheng, Zhongquan Charlie Zheng, and John S. Allen. "Time-domain simulation of acoustic wave scattering and internal propagation from a gas bubble of various shapes." Journal of the Acoustical Society of America 153, no. 3 (March 2023): 1468–79. http://dx.doi.org/10.1121/10.0017386.
Повний текст джерелаАнотація:
Acoustic scattering and resonances of gas bubbles are computed using a time-domain simulation based on numerical solutions of the conservation laws. The time histories of scattered pressure and fluid velocity, outside and inside the bubble, are obtained simultaneously from an immersed-boundary method allowing for the investigation of exterior and interior fields for non-spherical geometries. The acoustic resonances of the bubble are investigated for various bubble sizes, shapes, and inner gas parameters and compared in limiting cases to the partial wave scattering solutions for spherical bubbles. The dynamics of the gas motion and its associated contribution to resonance response has received little attention in previous analytical and numerical formulations. In this study, the acoustic propagation and motion inside the interior gas is investigated with respect to the monopole resonance with the combined time-domain simulation and immersed-boundary method. For the non-spherical prolate and oblate shapes, the scattering and resonance behaviors are compared with the approximate analytical results based on the shape factor method. The simulation method can be extended to less-understood shapes relevant to underwater and physical acoustics, such as “pancake-shaped” or “cigar-shaped” bubbles, as well as to spatial and time-dependent forcing.
11
Alhendal, Yousuf, and Ali Turan. "Thermocapillary bubble dynamics in a 2D axis swirl domain." Heat and Mass Transfer 51, no. 4 (September 17, 2014): 529–42. http://dx.doi.org/10.1007/s00231-014-1427-9.
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Dorman, V. L., V. L. Sobolev, and A. B. Shevchenko. "Bloch lines dynamics in domain wall of magnetic bubble." Journal of Magnetism and Magnetic Materials 124, no. 1-2 (June 1993): 221–27. http://dx.doi.org/10.1016/0304-8853(93)90091-f.
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Tejedor Sastre, María Teresa, and Christian Vanhille. "Nonlinear Resonance of Cavities Filled with Bubbly Liquids: A Numerical Study with Application to the Enhancement of the Frequency Mixing Effect." Shock and Vibration 2018 (December 6, 2018): 1–9. http://dx.doi.org/10.1155/2018/1570508.
Повний текст джерелаАнотація:
This paper studies the nonlinear resonance of a cavity filled with a nonlinear biphasic medium made of a liquid and gas bubbles at a frequency generated by nonlinear frequency mixing. The analysis is performed through numerical simulations by mixing two source signals of frequencies well below the bubble resonance. The finite-volume and finite-difference based model developed in the time domain simulates the nonlinear interaction of ultrasound and bubble dynamics via the resolution of a differential system formed by the wave and Rayleigh–Plesset equations. Some numerical results, consistent with the literature, validate our procedure. Other results reveal the existence of a frequency shift of the cavity resonance at the difference-frequency component, which rises with pressure amplitude and evidences the global changes undergone by the bubbly medium under finite amplitudes. Finally, this work shows the enhancement of the amplitude of the difference-frequency component generated by parametric excitation using the nonlinear resonance shift, which is more pronounced when the second primary frequency is constant, the first one is varied to match the nonlinear resonance, and both have the same amplitude.
14
Yang, Hung-Hsiang, Namrata Bansal, Philipp Rüßmann, Markus Hoffmann, Lichuan Zhang, Dongwook Go, Qili Li, et al. "Magnetic domain walls of the van der Waals material Fe3GeTe2." 2D Materials 9, no. 2 (March 23, 2022): 025022. http://dx.doi.org/10.1088/2053-1583/ac5d0e.
Повний текст джерелаАнотація:
Abstract Among two-dimensional materials, Fe3GeTe2 has come to occupy a very important place owing to its ferromagnetic nature with one of the highest Curie temperatures among known van der Waals materials and the potential for hosting skyrmions. In this combined experimental and theoretical work, we investigate the magnetic bubble domains as well as the microscopic domain wall profile using spin-polarized scanning tunneling microscopy in combination with atomistic spin-dynamics simulations performed with parameters from density functional theory calculations. We find a weak magneto-electric effect influencing the domain wall width by the electric field in the tunneling junction and determine the critical magnetic field for the collapse of the bubble domains. Our findings shed light on the origins of complex magnetism that Fe3GeTe2 exhibits.
15
Ye, Xi, Longquan Sun, and Fuzhen Pang. "Dynamics and noise radiation of multiple bubbles in compressible fluid using boundary integral equation." Engineering Computations 32, no. 3 (May 5, 2015): 885–913. http://dx.doi.org/10.1108/ec-01-2014-0007.
Повний текст джерелаАнотація:
Purpose – The purpose of this paper is to research the interaction between multiple bubbles and their noise radiation considering the influence of compressibility. The influences of bubble spacing, initial inner pressure, buoyance and phase difference are presented with different bubbles arrangements. Design/methodology/approach – Based on wave equation, the new boundary integral equation considering the compressibility is given by the matching between prophase and anaphase approximation of bubble motion and solved with boundary element method. The time-domain characteristics of noise induced by multiple bubbles are obtained by the moving boundary Kirchhoff integral equation. With the surface discretization and coordinate transformation, the bubbles surface is treated as a moving deformable boundary and noise source, and the integral is implemented on the surface directly. Findings – Numerical results show the manner of jet generation will be affected by the phase difference between bubbles. With the increasing of phase difference, the directive property of noise becomes obvious. With the enlargement of initial inner pressure, the sound pressure will arise at the early stage of expanding, and the increasing of buoyance parameter will reduce the sound pressure after the generation of jet. Since the consideration of compressibility, the oscillation amplitude of bubbles will be weakened. Originality/value – The paper could provide the reference for the research about the dynamics and noise characteristics of multiple bubbles in compressible fluid. And the new method based on boundary integral equation to simulate the multiple bubbles motion and noise radiation is presented.
16
Zeng, Lei, Daniel Velez, Jiacai Lu, and Gretar Tryggvason. "Numerical Studies of Disperse Three-Phase Fluid Flows." Fluids 6, no. 9 (September 6, 2021): 317. http://dx.doi.org/10.3390/fluids6090317.
Повний текст джерелаАнотація:
The dynamics of a three-phase gas–liquid–liquid multiphase system is examined by direct numerical simulations. The system consists of a continuous liquid phase, buoyant gas bubbles, and smaller heavy drops that fall relative to the continuous liquid. The computational domain is fully periodic, and a force equal to the weight of the mixture is added to keep it in place. The governing parameters are selected so that the terminal Reynolds numbers of the bubbles and the drops are moderate; while the effect of bubble deformability is examined by changing its surface tension, the surface tension for the drops is sufficiently high so they do not deform. One bubble in a “unit cell” and eight freely interacting bubbles are examined. The dependency of the slip velocities, the velocity fluctuations, and the distribution of the dispersed phases on the volume fraction of each phase are examined. It is found that while the distribution of drops around a single bubble in a “unit cell” is uneven and depends on its deformability, the distribution of drops around freely interacting bubbles is relatively uniform for the parameters examined in this study.
17
Krotenko, E. B., Yu A. Kuzin, Yu V. Melickov, A. M. Redchenko, and F. G. Baryakhtar. "Theory of domain wall dynamics in bubble films with coercivity." Journal of Magnetism and Magnetic Materials 136, no. 1-2 (September 1994): 59–64. http://dx.doi.org/10.1016/0304-8853(94)90446-4.
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Liu, Yunqiao, and Benlong Wang. "Dynamics and surface stability of a cylindrical cavitation bubble in a rectilinear vortex." Journal of Fluid Mechanics 865 (March 1, 2019): 963–92. http://dx.doi.org/10.1017/jfm.2019.103.
Повний текст джерелаАнотація:
In this paper, we formulate the dynamic equations of radial and surface modes for a cylindrical cavitation bubble subject to a prescribed uniform rectilinear vortex flow. The potential flow in the bulk volume of the external flow is modelled using the general mode decomposition approach. The stability of surface modes is investigated under linear analysis. The effects of confinement due to a limited flow domain in a water tunnel and viscosity at the bubble surface are evaluated, which can be fairly neglected for the cylindrical cavitation bubbles discussed. Our model is capable of predicting the developments of surface modes, which agrees well with experimental observations reported in the literature. We derive the Mathieu structure in the dynamic equation of the surface oscillation and the associated instability condition of the surface mode oscillations. The numerical results confirm that the Mathieu-type instability controls the stability diagrams and the emergence of surface modes under specific radial oscillation.
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Erchiqui, Fouad, Mhamed Souli, Toufik Kanit, Abdellatif Imad, Boudlal Aziz, and Ahmed El Moumen. "Characterization of Polymeric Membranes Under Large Deformations Using Fluid-Structure Coupling." International Journal of Applied Mechanics 07, no. 05 (October 2015): 1550068. http://dx.doi.org/10.1142/s1758825115500684.
Повний текст джерелаАнотація:
The mechanical properties of Ogden material under biaxial deformation are obtained by using the bubble inflation technique. First, pressure inside the bubble and height at the hemispheric pole are recorded during bubble inflation experiment. Thereafter, Ogden's theory of hyperelasticity is employed to define the constitutive model of flat circular thermoplastic membranes (CTPMs) and nonlinear equilibrium equations of the inflation process are solved using finite difference method with deferred corrections. As a last step, a neuronal algorithm artificial neural network (ANN) model is employed to minimize the difference between calculated and measured parameters to determine material constants for Ogden model. This technique was successfully implemented for acrylonitrile-butadiene-styrene (ABS), at typical thermoforming temperatures, 145°C. When solving for the bubble inflation, the recorded pressure is applied uniformly on the structure. During the process inflation, the pressure is not uniform inside the bubble, thus full gas dynamic equations need to be solved to get the appropriate nonuniform pressure to be applied on the structure. In order to simulate the inflation process accurately, computational fluid dynamics in a moving fluid domain as well as fluid structure interaction (FSI) algorithms need to be performed for accurate pressure prediction and fluid structure interface coupling. Fluid structure interaction solver is then required to couple the dynamic of the inflated gas to structure motion. Recent development has been performed for the simulation of gas dynamic in a moving domain using arbitrary Lagrangian Eulerian (ALE) techniques.
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Islam, Tariqul, P. Ganesan, J. N. Sahu, and F. A. Hamad. "Numerical study to invistigate the effect of inlet gas velocity and Reynolds number on bubble formation in a viscous liquid." Thermal Science 19, no. 6 (2015): 2127–38. http://dx.doi.org/10.2298/tsci140825015i.
Повний текст джерелаАнотація:
Bubble formation dynamics has great value in mineral recovery and the oil industry. In this paper, a single bubble formation process through an orifice in a rectangle domain is modelled to study the bubble formation characteristics using the volume of fluid (VOF) with the continuum surface force (CSF) method. The effect of gas inlet velocities, Ug ~ 0.1 - 0.3 m/s on bubble formation stages (i.e., expansion, elongation and pinch off), bubble contact angle, dynamics and static pressure, bubble departure diameter etc. was investigated through an orifice diameter of 1 mm. The method was also used to study the effect of Reynolds number, Re? ~ 1.32 - 120 on bubble formation when all other parameters were kept constant. It is found that a high inlet gas velocity accelerated the reducing of the bubble contact angle from an obtuse angle to an acute angle and the faster development of hemispherical shape of the bubble. It is also found that an increasing of Reynolds number caused speeding up of the bubble pinch-off and formed a smaller bubble neck height due to stronger vortex ring around the bubble neck.
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Tang, Hao, Yun-Long Liu, Pu Cui, and A. Man Zhang. "Numerical study on the bubble dynamics in a broken confined domain." Journal of Hydrodynamics 32, no. 6 (December 2020): 1029–42. http://dx.doi.org/10.1007/s42241-020-0078-1.
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Morrissey, R. P., M. Redjdal, M. F. Ruane, and F. B. Humphrey. "Numerical investigation of stripe domain dynamics in grooved bubble garnet films." Journal of Applied Physics 85, no. 8 (April 15, 1999): 6199–201. http://dx.doi.org/10.1063/1.370220.
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Hsiao, C. T., and G. L. Chahine. "Numerical Study of Cavitation Inception Due to Vortex/Vortex Interaction in a Ducted Propulsor." Journal of Ship Research 52, no. 02 (June 1, 2008): 114–23. http://dx.doi.org/10.5957/jsr.2008.52.2.114.
Повний текст джерелаАнотація:
Cavitation inception in a ducted propulsor was studied numerically using Navier-Stokes computations and bubble dynamics models. Experimental observations of the propulsor model and previous numerical computations using Reynolds-averaged Navier-Stokes (RANS) codes indicated that cavitation inception occurred in the region of interaction of the leakage and trailing tip vortices. The RANS simulations failed, however, to predict correctly both the cavitation inception index value and the inception location. To improve the numerical predictions, we complemented here the RANS computations with a direct Navier-Stokes simulation in a reduced computational domain including the region of interaction of the two vortices. Initial and boundary conditions in the reduced domain were provided by the RANS solution of the full ducted propulsor flow. Bubble nuclei were released in this flow field, and spherical and nonspherical bubble dynamics models were exercised to investigate cavitation inception. This resulted in a solution in much better agreement with the experimental measurements than the original RANS solution. Both the value of the cavitation inception index and the location of the cavitation inception were very well captured. The characteristics of the emitted acoustic signals and of the bubble shapes during a cavitation event were also computed.
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Gimaltdinov, I. K., A. A. Nasyrov, A. A. Gimaltdinova, A. A. Gizzatullina, M. N. Galimzyanov, and E. Yu Kochanova. "Focusing of a compression waves in a toroidal bubble cluster." Journal of Physics: Conference Series 2388, no. 1 (December 1, 2022): 012113. http://dx.doi.org/10.1088/1742-6596/2388/1/012113.
Повний текст джерелаАнотація:
Abstract The dynamics of waves in a cylindrical channel containing a toroidal bubble cluster is studied. It is shown that the existence of a cluster cause of focusing of waves in the channel. The dependence of the maximum amplitude of the compression wave formed in the domain on the parameters of the domain, as well as on the amplitude of the initial pulse, is analyzed.
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Yang, S. M., Z. C. Feng, and L. G. Leal. "Nonlinear effects in the dynamics of shape and volume oscillations for a gas bubble in an external flow." Journal of Fluid Mechanics 247 (February 1993): 417–54. http://dx.doi.org/10.1017/s0022112093000515.
Повний текст джерелаАнотація:
This paper considers the dynamics of a gas bubble in response to either a pressure pulse or a pressure step at t = 0, both in the presence and absence of a mean flow. Our work utilizes small-deformation, domain perturbation analysis carried to second and higher order in the amplitude of deformation, ε. In the absence of a mean flow, our analysis of the small deformation problem for an initial impulsive perturbation of the bubble volume and shape is closely related to recently published work by Longuet-Higgins on the time-dependent oscillations of an initially deformed bubble in a quiescent fluid. However, in the presence of a mean flow which deforms the bubble, the bubble response to pressure changes is more complex. Specifically, the present analysis identifies a number of different mechanisms for resonant interaction between shape deformation modes and the volume or radial breathing mode of oscillation. This includes not only a fundamental change in the resonant interactions at 0(ε2) - where resonant interaction is also found in the absence of mean flow – but resonant interactions also at the level of 0(ε3/2;) which are not present without the mean flow. On the other hand, the bubble dynamics in response to a step change in the pressure distribution in a quiescent fluid exhibits similar resonant interactions at 0(ε2) to those obtained for a pressure pulse in the presence of mean flow because the bubble oscillates around a non-spherical steady-state shape owing to the non-uniform pressure distribution on the bubble surface in both the cases.
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Ly, Hai-Bang, Eric Monteiro, Tien-Thinh Le, Vuong Minh Le, Morgan Dal, Gilles Regnier, and Binh Thai Pham. "Prediction and Sensitivity Analysis of Bubble Dissolution Time in 3D Selective Laser Sintering Using Ensemble Decision Trees." Materials 12, no. 9 (May 10, 2019): 1544. http://dx.doi.org/10.3390/ma12091544.
Повний текст джерелаАнотація:
The presence of defects like gas bubble in fabricated parts is inherent in the selective laser sintering process and the prediction of bubble shrinkage dynamics is crucial. In this paper, two artificial intelligence (AI) models based on Decision Trees algorithm were constructed in order to predict bubble dissolution time, namely the Ensemble Bagged Trees (EDT Bagged) and Ensemble Boosted Trees (EDT Boosted). A metadata including 68644 data were generated with the help of our previously developed numerical tool. The AI models used the initial bubble size, external domain size, diffusion coefficient, surface tension, viscosity, initial concentration, and chamber pressure as input parameters, whereas bubble dissolution time was considered as output variable. Evaluation of the models’ performance was achieved by criteria such as Mean Absolute Error (MAE), Root Mean Squared Error (RMSE) and coefficient of determination (R2). The results showed that EDT Bagged outperformed EDT Boosted. Sensitivity analysis was then conducted thanks to the Monte Carlo approach and it was found that three most important inputs for the problem were the diffusion coefficient, initial concentration, and bubble initial size. This study might help in quick prediction of bubble dissolution time to improve the production quality from industry.
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Yu, Jun, Hai-tao Li, Zhen-xin Sheng, Yi Hao, and Jian-hu Liu. "Numerical research on the cavitation effect induced by underwater multi-point explosion near free surface." AIP Advances 13, no. 1 (January 1, 2023): 015021. http://dx.doi.org/10.1063/5.0136546.
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In this study, the cavitation effect induced by two charges in underwater explosions near free surfaces is numerical researched by two dimensional compressible multiphase fluids based on a four-equation system with a phase transition model. The occurrence of the generation, development, and collapse of cavitation in two-charge underwater explosions near free surfaces can be captured directly. The detailed density, pressure, and vapor volume fraction contours during the interaction process are obtained and can better reveal the characteristic underlying the cavitation, free surface, and explosion bubbles. Numerical results reveal that the cavitation domain has expanded to an area much deeper than the explosion bubble location in two-charge underwater explosions, which should be paid enough attention due to its influence on the input load of underwater structures. The detailed density and pressure contours during the interaction process can also be captured and can better reveal the mechanism underlying the explosion bubble, cavitation, and surface wave dynamics. The present results can expand the currently limited database of multiphase fluid in underwater explosions and also provide new insights into the strong nonlinear interaction between underwater explosion and cavitation, which provides a deep understanding of multi-point explosions.
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Keshavarzi, Gholamreza, Ryan S. Pawell, and Tracie J. Barber. "Transient Analysis of Rising Bubble Using Image Analysis." Applied Mechanics and Materials 553 (May 2014): 162–67. http://dx.doi.org/10.4028/www.scientific.net/amm.553.162.
Повний текст джерелаАнотація:
Image analysis can play an important role in the validation and analysis of computational studies. Computational Fluid Dynamics (CFD) compared to experiments, has the advantage of detailed information analysis across the domain of interest. However, with detailed image analysis not only better detailed information can be extracted from experimental results, but also numerical methods and CFD can benefit from better detailed post processing information. In this paper, we show how image analysis may be applied to CFD data to better understand the results. More specifically, we simulate the transient behaviour of a 9 mm bubble rising in a 20 mm wide flow cell and extract the precise kinematics and characteristics of the bubble using image analysis. In order to better understand the kinematics of the bubble, we extract and plot the transient position and shape characteristics of the bubble. These parameters provide detailed comparison and analysis of the ability and differences of the interface capturing methods. This leads to better understanding of the applicability and accuracy of these models for various applications.
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Wang, Qianxi. "Local energy of a bubble system and its loss due to acoustic radiation." Journal of Fluid Mechanics 797 (May 17, 2016): 201–30. http://dx.doi.org/10.1017/jfm.2016.281.
Повний текст джерелаАнотація:
Energy concentration and loss due to a violent collapsing bubble are essential phenomena to many applications such as cavitation erosion, biomedical ultrasonics, sonochemistry, cavitation cleaning and underwater explosions. It has been generally known that the energy of a bubble system is radiated away as an acoustic wave and dissipated by viscosity. However, there is no study in the scientific literature on the time history of the energy of a bubble system in a compressible flow. Here we have introduced the local energy of a non-spherical bubble system, consisting of the energy of the interior gas, the interface and the exterior liquid in the inner asymptotic region. The local energy determines the local bubble and flow dynamics, including the concentration of energy, stress and momentum. We obtain a simple formula for the radiated energy associated with acoustic radiation in terms of the bubble volume history. We perform calculations of the energy history for a transient bubble in a compressible liquid in an infinite domain, subject to buoyancy and near a rigid boundary, respectively. Our calculations show that the local energy of a transient bubble follows a step function in time, being nearly conserved for most of each cycle of oscillation but decreasing rapidly and significantly at bubble inception and at the end of collapse, due to the emission of steep pressure waves or shock waves. The loss of the local energy of the bubble system due to the emission of steep pressure waves and the associated damping of the bubble oscillation are diminished by buoyancy effects and decrease with the buoyancy parameter. Similarly, the loss of the local energy of a bubble system is diminished by the presence of a rigid boundary and decreases with the proximity of the bubble to the boundary. We also analyse the energy concentration of single bubble sonoluminescence in a standing acoustic wave.
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Gradov, Dmitry Vladimirovich, Andrey Saren, Janne Kauppi, Kari Ullakko, and Tuomas Koiranen. "Auto-Aspirated DAF Sparger Study on Flow Hydrodynamics, Bubble Generation and Aeration Efficiency." Processes 8, no. 11 (November 19, 2020): 1498. http://dx.doi.org/10.3390/pr8111498.
Повний текст джерелаАнотація:
A novel auto-aspirated sparger is examined experimentally in a closed-loop reactor (CLR) at lab scale using particle image velocimetry, high-speed camera and oxygen mass transfer rate measurements. State-of-the-art 3D printing technology was utilized to develop the sparger design in stainless steel. An insignificant change in the bubble size distribution was observed along the aerated flow, proving the existence of a low coalescence rate in the constraint domain of the CLR pipeline. The studied sparger created macrobubbles evenly dispersed in space. In pure water, the produced bubble size distribution from 190 to 2500 μm is controlled by liquid flow rate. The bubble size dynamics exhibited a power-law function of water flow rate approaching a stable minimum bubble size, which was attributed to the ratio of the fast-growing energy of the bubble surface tension over the kinetic energy of the stream. Potentially, the stream energy can efficiently disperse higher gas flow rates. The oxygen transfer rate was rapid and depended on the water flow rate. The aeration efficiency below 0.4 kW/m3 was superior to the commonly used aerating apparatuses tested at lab scale. The efficient gas dissolution technology has potential in water treatment and carbon capture processes applications.
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Kosinski, R. "Domain wall dynamics in [110] oriented bubble film in the presence of in-plane magnetic fields." IEEE Transactions on Magnetics 23, no. 5 (September 1987): 3373–75. http://dx.doi.org/10.1109/tmag.1987.1065586.
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Lu, Jiacai, and Gretar Tryggvason. "Dynamics of nearly spherical bubbles in a turbulent channel upflow." Journal of Fluid Mechanics 732 (August 30, 2013): 166–89. http://dx.doi.org/10.1017/jfm.2013.397.
Повний текст джерелаАнотація:
AbstractThe dynamics of bubbles in upflow, in a vertical channel, is examined using direct numerical simulations (DNS), where both the flow and the bubbles are fully resolved. Two cases are simulated. In one case all the bubbles are of the same size and sufficiently small so they remain nearly spherical. In the second case, some of the small bubbles are coalesced into one large bubble. In both cases lift forces drive small bubbles to the wall, removing bubbles from the channel interior until the two-phase mixture is in hydrostatic equilibrium, and forming a bubble-rich wall layer. The same evolution has been seen in earlier DNS of bubbly upflows, but here the friction Reynolds number is higher (${\mathit{Re}}^{+ } = 250$). In addition to showing that the overall structure persists at higher Reynolds numbers, we show that the bubbles in the wall layer form clusters. The mechanism responsible for the clustering is explained and how bubbles move into and out of the wall layer is examined. The dynamics of the bubbles in the channel core is also compared with results obtained in fully periodic domains and found to be similar. The presence of the large bubble disrupts the wall layer slightly, but does not change the overall picture much, for the parameters examined here.
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Lugomer, Stjepan. "Nano-wrinkles, compactons, and wrinklons associated with laser-induced Rayleigh–Taylor instability: I. Bubble environment." Laser and Particle Beams 38, no. 2 (April 6, 2020): 101–13. http://dx.doi.org/10.1017/s0263034620000105.
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ABSTRACTWe study dynamics, structure and organization of the new paradigm of wavewrinkle structures associated with multipulse laser-induced RayleighTaylor (RT) instability in the plane of a target surface in the circumferential zone (C-zone) of the spot. Irregular target surface, variation of the fluid layer thickness and of the fluid velocity affect the nonlinearity and dispersion. The fluid layer inhomogeneity establishes local domains arranged (organized) in the «domain network». The traveling wavewrinkles become solitary waves and latter on become transformed into stationary soliton wavewrinkle patterns. Their morphology varies in the radial direction ofaussian-like spot ranging from the compacton-like solitons to the aperiodic rectangular waves (with rounded top surface) and to the periodic ones. These wavewrinkles may be successfully juxtapositioned with the exact solution of the nonlinear differential equations formulated in the KadomtsevPetviashvili sense taking into account the fluid conditions in particular domain. The cooling wave that starts at the periphery by the end of the pulse causes sudden increase of density and surface tension: the wavewrinkle structures become unstable what causes their break-up. The onset of solidification causes formation of an elastic sheet which starts to shrink generating lateral tension on the wavewrinkles. The focusing of energy at the constrained boundary causes the formation of wrinklons as the new elementary excitation of the elastic sheets.
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Hegedűs, Ferenc, Péter Krähling, Werner Lauterborn, Robert Mettin, and Ulrich Parlitz. "High-performance GPU computations in nonlinear dynamics: an efficient tool for new discoveries." Meccanica 55, no. 12 (March 23, 2020): 2493–504. http://dx.doi.org/10.1007/s11012-020-01146-w.
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AbstractThe main aim of this paper is to demonstrate the benefit of the application of high-performance computing techniques in the field of non-linear science through two kinds of dynamical systems as test models. It is shown that high-resolution, multi-dimensional parameter scans (in the order of millions of parameter combinations) via an initial value problem solver are an efficient tool to discover new features of dynamical systems that are hard to find by other means. The employed initial value problem solver is an in-house code written in C++ and CUDA C software environments, which can exploit the high processing power of professional graphics cards (GPUs). The first test model is the Keller–Miksis equation, a non-linear oscillator describing the dynamics of a driven single spherical gas bubble placed in an infinite domain of liquid. This equation is important in the field of cavitation and sonochemistry. Here, the high-resolution parameter scans gave us the opportunity to lay down the basis of a non-feedback technique to control multi-stability in which direct selection of the desired attractor is possible. The second test model is related to a pressure relief valve that can exhibit a special kind of impact dynamics called grazing impact. A fine scan of the initial conditions revealed a second focal point of the grazing lines in the initial-condition space that was hidden in previous studies.
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Feng, Z. C., and L. G. Leal. "Bifurcation and chaos in shape and volume oscillations of a periodically driven bubble with two-to-one internal resonance." Journal of Fluid Mechanics 266 (May 10, 1994): 209–42. http://dx.doi.org/10.1017/s0022112094000984.
Повний текст джерелаАнотація:
We study the dynamic sof gas or vapour bubbles when the volume mode of oscillation is coupled with one of the shape modes through quadratic resonance. In particular, the frequency ratio of the volume mode and the shape mode is assumed to be close to two-to-one. The analysis is based upon the use of a two-timescale asymptotic approximation, combined with domain perturbation theory. The viscous effect of the fluid is included by using a rigorous treatment of weak viscosity. Through solvability conditions, amplitude equations governing the slow-timescale dynamics of the resonant modes are obtained. Bifurcation analysis of these amplitude equations reveals interesting phenomena. When volume oscillations are forced by oscillations of the external pressure, we find that the volume mode may lose stability for sufficiently large amplitudes of oscillation, and this instability may lead to chaotic oscillations of both the volume and the shape modes. However, we find that for chaos to occur, a critical degree of detuning is required between the shape and volume modes, in the sense that their natural frequencies must differ by more than a critical value. When a shape mode is forced by oscillations of anisotropic components of the external pressure, we find that chaos can occur even for exact resonance of the two modes. The physical significance of this result is also given.
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Yan, Di, Ahmed Kovacevic, Qian Tang, and Sham Rane. "Numerical investigation of cavitation in twin-screw pumps." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 20 (December 5, 2017): 3733–50. http://dx.doi.org/10.1177/0954406217740927.
Повний текст джерелаАнотація:
In order to investigate the flow characteristics and the formation process of cavitation in twin-screw pumps, three-dimensional computational fluid dynamics numerical analysis has been carried out. A conformal structured moving mesh generated by an in-house code SCORG was applied for the rotor domain. The volume of fluid method has been adopted for dealing with the liquid-gas two-phase flow, while the bubble dynamics was handled by a homogenous cavitation model. By changing the rotation speed and discharge pressure, the intensity, distribution area and variation of cavitation at different rotor angle were obtained. The effects of rotation speed and discharge pressure on cavitation characteristics have been analysed. Calculation results with cavitation model are compared with the results without cavitation and the experimentally obtained values. The influence of cavitation on the performance of a screw pump in terms of the mass flow rate, pressure distribution, rotor torque and the shaft power has been analysed and discussed. For analysis of cavitation in clearances, a 2D numerical model which includes radial and inter-lobe clearances was used. The relationship between volumetric efficiency and cavitation intensity was developed by variation of boundary conditions.
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Rezakazemi, Mashallah, and Saeed Shirazian. "Gas-Liquid Phase Recirculation in Bubble Column Reactors: Development of a Hybrid Model Based on Local CFD – Adaptive Neuro-Fuzzy Inference System (ANFIS)." Journal of Non-Equilibrium Thermodynamics 44, no. 1 (January 28, 2019): 29–42. http://dx.doi.org/10.1515/jnet-2018-0028.
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Abstract The Euler–Euler method and soft computing methods are recently utilized for the purpose of bubbly flow simulation and evolution of the dispersed and continuous phase in a two-phase reactor. Joining computational fluid dynamics (CFD) to the adaptive neuro-fuzzy inference system (ANFIS) method can enable the researchers to avoid several runs for heavy numerical methods (multidimensional Euler–Euler) to optimize fluid conditions. This overview can also help the researchers to carefully analyze fluid conditions and categorize their huge number of data in their artificial neural network nodes and avoid a complex non-structure CFD mesh. In addition, it can provide a neural geometry without limitation of an increasing mesh number in the fluid domain. In this study, gas and liquid circulation were considered as one of the main CFD factors in the scale-up of reactors used as an output parameter for prediction tool (ANFIS method) in different dimensions. This study shows that a combination of ANFIS and CFD methods provides the non-discrete domain in various dimensions and makes a smart tool to locally predict multiphase flow. The integration of numerical calculation and smart methods also shows that there is a great agreement between CFD results and ANFIS output depending on different dimensions.
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Zhang, Bei Chen, Qing Lian Li, Yuan Wang, and Jian Qiang Zhang. "Analysis of Two-Phase Pressure Drop Fluctuation Characteristics in a Single Mini-Channel." Defect and Diffusion Forum 366 (April 2016): 151–56. http://dx.doi.org/10.4028/www.scientific.net/ddf.366.151.
Повний текст джерелаАнотація:
Two-phase pressure drop fluctuations during flow boiling in a single mini-channel were experimentally investigated. Degassed water was tested in circular cross section mini-channels with the hydraulic diameter of 1.0 mm at liquid mass fluxes range of 21.19-84.77 kg m-2 s-1 and heat fluxes of 0~155.75 kW m-2. Effects of heat flux and mass flux on pressure drop fluctuations were discussed based on the time and frequency domain analysis of the measured pressure drop. Two types of fluctuations were identified, which are the incipient boiling fluctuation (IBF) and the explosive boiling fluctuation (EBF) respectively. The IBF is a low frequency low amplitude fluctuation, which relates to the bubble dynamics when incipient boiling occurs. It is sensitive to the thermal and flow conditions. With the increase of heat flux and mass flux, the IBF is suppressed. The EBF is a low frequency high amplitude fluctuation, which occurs near the critical heat flux.
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Macdonald, C. A., and J. Gomatam. "Chaotic dynamics of microbubbles in ultrasonic fields." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 220, no. 3 (March 1, 2006): 333–43. http://dx.doi.org/10.1243/095440606x79596.
Повний текст джерелаАнотація:
Chaos is present in non-linear systems that describe temporal phenomena in the physical and life sciences. Well-known instances of chaos include the logistic map, the Lorenz equations, and forced non-linear oscillators. The regular and chaotic dynamics of free gas bubbles and gas-encapsulated microbubbles (contrast agents) are of immense importance in the efficient implementation of ultrasonic contrast imaging. A modification of the Keller-Herring model, which takes into account the elastic properties of the encapsulating shell, is investigated with respect to the bifurcation structure of the time-dependent microbubble radius. Numerical simulations show that the radial oscillations can be periodic as well as chaotic in appropriate parameter domains. Several investigations on chaotic aspects of dynamics presented here are new and highlighted appropriately. The influence of the acoustic field and shell parameters are investigated to identify values where the oscillations undergo bifurcations and the bubble response becomes chaotic. An analysis of chaotic behaviour in multiple-bubble systems completes the investigation and reveals the significant influence the free gas bubbles have on the acoustic response of their encapsulated counterparts.
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Chen, Nan, Xiyu Chen, and Antonio Delgado. "Numerical Study of Formation of a Series of Bubbles from an Orifice by Applying Dynamic Contact Angle Model." Advances in Materials Science and Engineering 2020 (October 30, 2020): 1–17. http://dx.doi.org/10.1155/2020/5213234.
Повний текст джерелаАнотація:
The dynamic contact angle model is applied in the formation process of a series of bubbles from Period-I regime to Period-II regime by using the VOF method on a 2D axisymmetric domain. In the first process of the current research, the dynamic contact angle model is validated by comparing the numerical results to the experimental data. Good agreement in terms of bubble shape and bubble detachment time is observed from a lower flow rate Q = 150.8 cm3/min (Re = 54.77, Period-I regime) to a higher flow rate Q = 603.2 cm3/min (Re = 219.07, Period-III regime). The comparison between the dynamic contact angle model and the static contact angle model is also performed. It is observed that the static contact angle model can obtain similar results as the dynamic contact angle model only for smaller gas flow rates (Q ≤ 150.8 cm3/min and Re ≤ 54.77)). For higher gas flow rates, the static contact angle model cannot produce good results as the dynamic contact angle model and has larger relative errors in terms of bubble detachment time and bubble shape.
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Juluru Sandeep and AVSS Kumara Swami Gupta. "Grid Adaptive Technique for Simulation of Scramjet Intake-Isolator at Hypersonic Speeds." Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 101, no. 1 (January 18, 2023): 73–89. http://dx.doi.org/10.37934/arfmts.101.1.7389.
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Hypersonic intake is one of the major components of Scramjet engine. It compresses the incoming hypersonic flow through a series of oblique shocks as the flow passes through intake-isolator section before entering the combustion chamber, which is essential for efficient combustion. The shocks generated inside in the intake interacts with boundary layer following shock boundary layer interaction and flow separation. The separated flow blocks the flow capture area such that engine expresses unstarting phenomenon. Understanding and mitigating such flow phenomenon is a challenging task. With respect to hypersonic speeds the experimental facilities are very limited. The only alternative to solve this problem is Computational Fluid Dynamics because of its capabilities. But validation of CFD results with analytical or experimental is the foremost prerequisite to chase computational analysis. Mostly at high speeds the precision of CFD results rest on the type of grid, number of elements and turbulence model used. So, in this paper, computational analysis of hypersonic intake is carried out through designed conditions to ensure the correct CFD process is used by varying number of elements in fluid domain by grid adaptive technique using ANSYS Fluent and satisfying Y+ parameter. The domain is analysed with various turbulence models and among them SST has predicted all the flow characteristics of scramjet intake-isolator at hypersonic speeds like separation bubble, shock reattachment, cowl shock etc similar to experimental results with the help of grid adaptive technique. So, grid adaptive technique is also proposed for simulation of scramjet intake at off-design conditions.
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Vakhrushev, Alexander, Ebrahim Karimi-Sibaki, Jan Bohacek, Menghuai Wu, Andreas Ludwig, Yong Tang, Gernot Hackl, Gerald Nitzl, Josef Watzinger, and Abdellah Kharicha. "Impact of Submerged Entry Nozzle (SEN) Immersion Depth on Meniscus Flow in Continuous Casting Mold under Electromagnetic Brake (EMBr)." Metals 13, no. 3 (February 21, 2023): 444. http://dx.doi.org/10.3390/met13030444.
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Complex multi-phase phenomena, including turbulent flow, solidification, and magnetohydrodynamics (MHD) forces, occur during the continuous casting (CC) under the applied electromagnetic brake (EMBr). The results of the small-scale experiment of the liquid metal model for continuous casting (mini-LIMMCAST) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), investigating MHD flow with a deep immersion depth of 100 mm, are supplemented by newly presented numerical studies with the shallow position of the submerged entry nozzle (SEN) at 50 mm below the meniscus. Herein, the focus is on the MHD effects at the meniscus level considering (i) a fully insulating domain boundary, (ii) a perfectly conductive mold, or (iii) the presence of the solid shell. The volume-of-fluid (VOF) approach is utilized to model a Galinstan flow, including free surface behavior. A multiphase solver is developed using conservative MHD formulations in the framework of the open-source computational fluid dynamics (CFD) package OpenFOAM®. The wall-adapting local eddy-viscosity (WALE) subgrid-scale (SGS) model is employed to model the turbulent effects on the free surface flow. We found that, for the deep immersion depth, the meniscus remains calm under the EMBr for the conductive and semi-conductive domain. For the insulated mold disregarding the SEN position, the self-inducing MHD vortices, aligned with the magnetic field, cause strong waving of the meniscus and air bubble entrapment for shallow immersion depth. Secondary MHD structures can form close to the meniscus under specific conditions. The influence of the EMBr and immersion depth on the flow energy characteristics is analyzed using power spectral density (PSD).
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Koken, Mete, Ismail Aydin, and Akis Sahin. "Application of computational fluid dynamics to predict hydrodynamic downpull on high head gates." Engineering Computations 34, no. 4 (June 12, 2017): 1191–203. http://dx.doi.org/10.1108/ec-04-2016-0137.
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Purpose High head gates are commonly used in hydropower plants for flow regulation and emergence closure. Hydrodynamic downpull can be a critical parameter in design of the lifting mechanism. The purpose of this paper is to show that a simplified two-dimensional (2D) computational fluid dynamics solution can be used in the prediction of the downpull force on the gate lip by comparison of computed results to experimentally measured data. Design/methodology/approach In this study, ANSYS FLUENT CFD software was used to obtain 2D numerical solution for the flow field around a generic gate model located in a power intake structure which was previously used in an experimental study. Description of the flow domain, computational grid resolution, requirements on setting appropriate boundary conditions and methodology in describing downpull coefficient are discussed. Total number of 245 simulations for variable gate lip geometry and gate openings were run. The downpull coefficient evaluated from the computed pressure field as function of gate opening and lip angle are compared with the experimental results. Findings The computed downpull coefficient agrees well with the previous experimental results, except one gate with small lip angle where a separation bubble forms along the lip, which is responsible from this deviation. It is observed that three-dimensional (3D) effects are confined to the large gate openings where downpull is minimum or even reversed. Research limitations/implications In large gate openings, three dimensionality of the flow around gate slots plays an important role and departure from 2D solutions become more pronounced. In that case, one might need to perform a 3D solution instead. Practical implications This paper presents a very fast and accurate way to predict downpull force on high head gates in the absence of experimental data. Originality/value An extensive amount of simulations are run within the scope of this study. It is shown that knowing its limitations, 2D numerical models can be used to calculate downpull for a wide range of gate openings without the need of expensive experimental models.
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McBain, Geordie Drummond. "Three ways to compute multiport inertance." ANZIAM Journal 60 (August 26, 2019): C140—C155. http://dx.doi.org/10.21914/anziamj.v60i0.14058.
Повний текст джерелаАнотація:
The immediate impulse-response of a confined incompressible fluid is characterized by inertance. For a vessel with one inlet and outlet, this is a single quantity; for multiple ports the generalization is a singular reciprocal inertance matrix which acts on the port-impulses to give the corresponding inflows. The reciprocal inertance coefficients are defined by the boundary fluxes of potential flows. Green's identity converts these coefficients to domain integrals of kinetic energy. For a system discretized with finite elements, a third method is proposed for computing reciprocal inertance coefficients which requires only the stiffness matrix and the solution vectors and no numerical differentiation.
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Sarath, K. P., and K. V. Manu. "An investigation of bluff body flow structures in variable velocity flows." Physics of Fluids 34, no. 3 (March 2022): 034102. http://dx.doi.org/10.1063/5.0083743.
Повний текст джерелаАнотація:
The present study explores three-dimensional vortex-dynamics past a wall-attached bluff body kept in a variable velocity field with numerical simulations. A trapezoidal pulse of mean velocity, consisting of acceleration phase from rest followed by constant velocity phase and deceleration phase to rest, is imposed at the inlet of the computational domain similar to the experimental study of Das et al. [“Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body,” J. Fluids Struct. 40, 233–245 (2013)]. For a wide range of Reynolds numbers ([Formula: see text]), acceleration Reynolds numbers ([Formula: see text]), and deceleration Reynolds numbers ([Formula: see text]), different stages of flow evolution are systematically analyzed. The flow evolution starts with the formation of a primary vortex followed by a two-dimensional circular array of spanwise vortex tubes by inflectional shear-layer instability. At a sufficiently high Reynolds number, the shear layer vortices originated from two-dimensional fluctuations deformed by three-dimensional instabilities, giving fragmented streamwise vorticity. In addition, long-wavelength “tongue-like structures” and short-wavelength “rib-like structures” are evident near the top wall and the bluff body, respectively. The streamwise vorticity generation equation indicates that the spanwise vortex tubes initially tilt, resulting in streamwise vorticity, further amplified by the vortex stretching process. The distinct flow features, including mode shape, frequency, and growth rate associated with the shear-layer instability, are identified using the dynamic mode decomposition (DMD) algorithm. Using the maximum growth rate criteria, the DMD technique successfully separates the coherent shear layer modes associated with two-dimensional shear layer instability from the flow field.
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Magnaudet, Jacques. "A ‘reciprocal’ theorem for the prediction of loads on a body moving in an inhomogeneous flow at arbitrary Reynolds number." Journal of Fluid Mechanics 689 (October 20, 2011): 564–604. http://dx.doi.org/10.1017/jfm.2011.363.
Повний текст джерелаАнотація:
AbstractSeveral forms of a theorem providing general expressions for the force and torque acting on a rigid body of arbitrary shape moving in an inhomogeneous incompressible flow at arbitrary Reynolds number are derived. Inhomogeneity arises because of the presence of a wall that partially or entirely bounds the fluid domain and/or a non-uniform carrying flow. This theorem, which stems directly from Navier–Stokes equations and parallels the well-known Lorentz reciprocal theorem extensively employed in low-Reynolds-number hydrodynamics, makes use of auxiliary solenoidal irrotational velocity fields and extends results previously derived by Quartapelle & Napolitano (AIAA J., vol. 21, 1983, pp. 911–913) and Howe (Q. J. Mech. Appl. Maths, vol. 48, 1995, pp. 401–426) in the case of an unbounded flow domain and a fluid at rest at infinity. As the orientation of the auxiliary velocity may be chosen arbitrarily, any component of the force and torque can be evaluated, irrespective of its orientation with respect to the relative velocity between the body and fluid. Three main forms of the theorem are successively derived. The first of these, given in (2.19), is suitable for a body moving in a fluid at rest in the presence of a wall. The most general form (3.6) extends it to the general situation of a body moving in an arbitrary non-uniform flow. Specific attention is then paid to the case of an underlying time-dependent linear flow. Specialized forms of the theorem are provided in this situation for simplified body shapes and flow conditions, in (3.14) and (3.15), making explicit the various couplings between the body’s translation and rotation and the strain rate and vorticity of the carrying flow. The physical meaning of the various contributions to the force and torque and the way in which the present predictions reduce to those provided by available approaches, especially in the inviscid limit, are discussed. Some applications to high-Reynolds-number bubble dynamics, which provide several apparently new predictions, are also presented.
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Choi, S. J., F. X. Giraldo, J. Kim, and S. Shin. "Verification of a non-hydrostatic dynamical core using the horizontal spectral element method and vertical finite difference method: 2-D aspects." Geoscientific Model Development 7, no. 6 (November 19, 2014): 2717–31. http://dx.doi.org/10.5194/gmd-7-2717-2014.
Повний текст джерелаАнотація:
Abstract. The non-hydrostatic (NH) compressible Euler equations for dry atmosphere were solved in a simplified two-dimensional (2-D) slice framework employing a spectral element method (SEM) for the horizontal discretization and a finite difference method (FDM) for the vertical discretization. By using horizontal SEM, which decomposes the physical domain into smaller pieces with a small communication stencil, a high level of scalability can be achieved. By using vertical FDM, an easy method for coupling the dynamics and existing physics packages can be provided. The SEM uses high-order nodal basis functions associated with Lagrange polynomials based on Gauss–Lobatto–Legendre (GLL) quadrature points. The FDM employs a third-order upwind-biased scheme for the vertical flux terms and a centered finite difference scheme for the vertical derivative and integral terms. For temporal integration, a time-split, third-order Runge–Kutta (RK3) integration technique was applied. The Euler equations that were used here are in flux form based on the hydrostatic pressure vertical coordinate. The equations are the same as those used in the Weather Research and Forecasting (WRF) model, but a hybrid sigma–pressure vertical coordinate was implemented in this model. We validated the model by conducting the widely used standard tests: linear hydrostatic mountain wave, tracer advection, and gravity wave over the Schär-type mountain, as well as density current, inertia–gravity wave, and rising thermal bubble. The results from these tests demonstrated that the model using the horizontal SEM and the vertical FDM is accurate and robust provided sufficient diffusion is applied. The results with various horizontal resolutions also showed convergence of second-order accuracy due to the accuracy of the time integration scheme and that of the vertical direction, although high-order basis functions were used in the horizontal. By using the 2-D slice model, we effectively showed that the combined spatial discretization method of the spectral element and finite difference methods in the horizontal and vertical directions, respectively, offers a viable method for development of an NH dynamical core.
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Cheng, Yixuan, Qiong Zhang, Pan Jiang, Kaidi Zhang, and Wei Wei. "Investigation of Plume Offset Characteristics in Bubble Columns by Euler–Euler Simulation." Processes 8, no. 7 (July 7, 2020): 795. http://dx.doi.org/10.3390/pr8070795.
Повний текст джерелаАнотація:
Based on low-cost and easy to enlarge, the bubble column device has been widely concerned in chemical industry. This paper focuses on bubble plumes in laboratory-scale three-dimensional rectangular air-water columns. Static behavior has been investigated in many experiments and simulations, and our present investigations consider the dynamic behavior of bubble plume offset in three dimensions. The investigations are conducted with a set of closure models by the Euler–Euler approach, and subsequently, literature data for rectangular bubble columns are analyzed for comparison purposes. Moreover, the transient evolution characteristics of the bubble plume in the bubble column and the gas phase distribution in sections are introduced, and the offset characteristics and the oscillation period of the plume are analyzed. In addition, the distributions of the vector diagram of velocity and vortex intensity in the domain are given. The effects of different fluxes and column aspect ratios on bubble plumes are studied, and the offset and plume oscillation period (POP) characteristics of bubbles are examined. The investigations reveal quantitative correlations of operating conditions (gas volume flux) and aspect ratios that have not been reported so far, and the simulated and experimental POP results agree well. An interesting phenomenon is that POP does not occur under conditions of a high flux and aspect ratio, and the corresponding prediction values for the conditions with and without POP are given as well. The results reported in this paper may open up a new way for further study of the mass transfer of bubble plumes and development of chemical equipment.
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WONG, HARRIS, DAVID RUMSCHITZKI, and CHARLES MALDARELLI. "Theory and experiment on the low-Reynolds-number expansion and contraction of a bubble pinned at a submerged tube tip." Journal of Fluid Mechanics 356 (February 10, 1998): 93–124. http://dx.doi.org/10.1017/s0022112097007805.
Повний текст джерелаАнотація:
The expansion and contraction of a bubble pinned at a submerged tube tip and driven by constant gas flow rate Q are studied both theoretically and experimentally for Reynolds number Re[Lt ]1. Bubble shape, gas pressure, surface velocities, and extrapolated detached bubble volume are determined by a boundary integral method for various Bond (Bo=ρga2/σ) and capillary (Ca=μQ/σa2) numbers, where a is the capillary radius, ρ and μ are the liquid density and viscosity, σ is the surface tension, and g is the gravitational acceleration.Bubble expansion from a flat interface to near detachment is simulated for a full range of Ca (0.01–100) and Bo (0.01–0.5). The maximum gas pressure is found to vary almost linearly with Ca for 0.01[les ]Ca[les ]100. This correlation allows the maximum bubble pressure method for measuring dynamic surface tension to be extended to viscous liquids. Simulated detached bubble volumes approach static values for Ca[Lt ]1, and asymptote as Q3/4 for Ca[Gt ]1, in agreement with analytic predictions. In the limit Ca→0, two singular time domains are identified near the beginning and the end of bubble growth during which viscous and capillary forces become comparable.Expansion and contraction experiments were conducted using a viscous silicone oil. Digitized video images of deforming bubbles compare well with numerical solutions. It is observed that a bubble contracting at high Ca snaps off.
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Padhi, Payodhar, Biranchi Narayan Dash, Pragyan Mohanty, B. K. Satapathy, and Sachikanta Kar. "Synthesis of Bulk Metal Matrix Nanocomposites by Full Cavitation Solidification Method." Key Engineering Materials 545 (March 2013): 193–96. http://dx.doi.org/10.4028/www.scientific.net/kem.545.193.
Повний текст джерелаАнотація:
There are several methods for the production of metal matrix nano composites including mechanical alloying, vertex process and spray deposition. However, the above processes are expensive. Solidification processing is a relatively cheaper route. However, during solidification processing nano particulates tend to agglomerate as a result of van der Waals forces and thus proper dispersion of the nano-particulate in metal matrix is a challenge. Many researchers dispersed nanoparticles in metal matrix by ultrasonic casting. However their technique has several drawbacks such as the oscillating probe, which is in direct contact with liquid metal, may dissolve in the liquid metal and contaminate it. Moreover, the extent of dispersion is not uniform. It is maximum near the probe and gradually decreases as one move away from the probe. Lastly in the method developed by them, the oscillating probe is removed from the liquid metal before cooling and solidification begin. It may lead to partial reagglomeration of nanoparticles. To overcome these difficulties a non-contact method, where the ultrasonic probe is not in direct contact with the liquid metal, was attempted to disperse Nano-sized Al2O3 particulates in aluminium matrix. In this method the mold was subjected to ultrasonic vibration. The crystallite size of Al2O3 was mostly below 10 nm. Nano composite having 1-1.5 wt. % of Al2O3 was cast. From HRTEM studies it is observed that the Al2O3 particles are distributed uniformly except the grain boundaries. In micro scale the hardness is uniform throughout the samples. This is due to cavitation process as well as pushing of the nano-particles during the growth of the grains. In the present study it accounts all first-order effects i.e., phase change, bubble dynamics, turbulent pressure fluctuations, and noncondensable gases for deaglomeration and distribution of particles throughout the domain to get uniform distributions.